Connection statuses

[K Young]

Hello, I've been reading through nginx source to understand the metrics
<http://nginx.org/en/docs/http/ngx_http_stub_status_module.html> that are
reported. I've got an idea of what is happening, but since the flow is
asynchronous, I'm not 100% confident, and would love your feedback.

Is the following correct?

   - 'accepts' is incremented when a worker gets a new request for a
   connection from the OS
   - 'handled' is incremented when a worker gets a new connection for a
   request


And then once a connection is opened:

   - 'active' is incremented (actually, it is incremented right before
   'handled', but will be decremented if the worker doesn't handle the
   connection request).
   - then the connection briefly goes into a waiting state while the
   request is waiting to be processed
   - then the connection goes into a short reading state while request
   headers are read. Simultaneously, 'request' is incremented every time a new
   request header begins to be read.
   - then the connection goes into a writing state while all work is done
   by nginx and by upstream components
   - then if the connection will be kept alive, it goes back into waiting
   state, which is synonymous with 'idle'
   - finally when the connection is closed, active is decremented

The things I'm least certain of about the 'waiting' state:

   - Does active always sum up to waiting+reading+writing?
   - Does each new connection enter a waiting state just before it goes
   into the reading state?
   - While waiting for upstream responses, is the connection in writing
   state or waiting state?
   - While waiting for new client requests on an open connection, is the
   connection in a waiting state?

Is the attached sketch of the above connection states correct? (underneath
"READ" it says "request++" to indicate that this is where the request
counter gets incremented).
[image: Inline image 1]

Thanks very much in advance for any help you can provide,
~K
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